Measuring the diaspora for virus-specific CD8+ T cells

Abstract

The CD8(+) T cell diaspora has been analyzed after secondary challenge with an influenza A virus that replicates only in the respiratory tract. Numbers of D(b)NP(366)- and D(b)PA(224)-specific CD8(+) T cells were measured by tetramer staining at the end of the recall response, then followed sequentially in the lung, lymph nodes, spleen, blood, and other organs. The extent of clonal expansion did not reflect the sizes of the preexisting memory T cell pools. Although the high-frequency CD8(+) tetramer(+) populations in the pneumonic lung and mediastinal lymph nodes fell rapidly from peak values, the "whole mouse" virus-specific CD8(+) T cell counts decreased only 2-fold over the 4 weeks after infection, then subsided at a fairly steady rate to reach a plateau at about 2 months. The largest numbers were found throughout in the spleen, then the bone marrow. The CD8(+)D(b)NP(366)+ and CD8(+)D(b)PA(224)+ sets remained significantly enlarged for at least 4 months, declining at equivalent rates while retaining the nucleoprotein > acid polymerase immunodominance hierarchy characteristic of the earlier antigen-driven phase. Lowest levels of the CD69 "activation marker" were detected consistently on virus-specific CD8(+) T cells in the blood, then the spleen. Those in the bone marrow and liver were intermediate, and CD69(hi) T cells were very prominent in the regional lymph nodes and the nasal-associated lymphoid tissue. Any population of "resting" CD8(+) memory T cells is thus phenotypically heterogeneous, widely dispersed, and subject to broad homeostatic and local environmental effects irrespective of epitope specificity or magnitude.

Figure 1

Expansion and maintenance of the immunodominant CD8⁺D^bNP₃₆₆⁺ T cells. It is important to note that the scales on the y axis differ for A–E. The results for lymphocyte populations recovered directly from the site of virus-induced pathology (BAL and lung) are grouped with those for the draining LNs (MLN and cervical LN, the latter included in the SLNs) in A and B, and the findings for the other sites sampled are shown in B, D, and E. Cell numbers (B, D, and E) were calculated from the frequencies (A and C) and the total CD8⁺ T cell counts (data not shown) for the particular organ. Epitope-specific CD8⁺ T cell counts for the spleen were generally 10-fold higher than for any other tissue. * denotes that the frequencies (A and C) were significantly higher in these samples than in the MLN throughout the course of the experiment.

Figure 2

Quantitative analysis of the CD8⁺D^bPA₂₂₄⁺ T cell response and memory. The data are presented exactly as described in the legend to Fig. 1. The y axis scales for A–E differ and also differ from those in the comparable panels in Fig. 1.

Figure 3

Distribution profiles of CD69^hi virus-specific CD8⁺ T cells. The frequency analysis for the CD69^hiCD8⁺D^bNP₃₆₆⁺ populations is presented in A and B and for the CD69^hiCD8⁺D^bPA₂₂₄⁺ sets in C and D. As described in the legend to Fig. 1, the results for sites associated directly with the pneumonic lung are shown in A and C, and the findings for the blood, BM, and other solid tissues are in B and D. The scales on the y axis differ for A–D.